Pancreatobiliary-type intraductal papillary mucinous neoplasm of the pancreas may have 2 subtypes with distinct clinicopathologic and genetic features.

We recently experienced cases of pancreatobiliary-type intraductal papillary mucinous neoplasms (PB-IPMNs) with imaging features resembling pancreatic ductal adenocarcinomas (PDACs), and histologic appearance of purely pancreatobiliary morphology and highly distorted papillary growth, which led to the present study aiming to systematically investigate PB-IPMNs in comparison with PDACs. Surgical cases of PB-IPMNs (n = 31) and PDACs (n = 24) were examined. PB-IPMNs were classified into monotypic tumors (n = 12; 39%) consisting of entirely high-grade pancreatobiliary-type neoplastic cells and polytypic cases (n = 19; 61%) associated with components of low-grade dysplasia and/or other histologic types (eg, gastric, intestinal, or oncocytic types). Clinically, monotypic PB-IPMNs less commonly had dilatation of the ampullary orifice (0% versus 74%) and mucin hypersecretion (17% versus 89%) than did polytypic cases. In most cases of monotypic PB-IPMNs, cystic dilatation of the lesional ducts was less obvious on imaging; therefore, 33% were radiologically diagnosed as PDACs. Histologically, intraductal tumors in monotypic cases showed a highly complex papillary architecture with tubular/cribriform glands and irregular branching, and all these cases were associated with invasive malignancy. GNAS mutations were detected in polytypic PB-IPMNs (6/19; 32%), but there were no GNAS mutations in monotypic cases. The recurrence-free survival of patients with monotypic PB-IPMN or PDAC was similar and significantly worse than that of patients with polytypic PB-IPMN. In conclusion, some cases of monotypic PB-IPMNs lacked the classic characteristics of IPMNs and shared features with PDACs, raising the possibility that these cases may be better classified as a papillary variant of PDACs rather than IPMNs.